code: def value(self, obs_n, act_n):
      inputs = layers.concat(obs_n + act_n, axis=1)
      hid1 = self.fc1(inputs)
      hid2 = self.fc2(hid1)
      Q = self.fc3(hid2)
      Q = layers.squeeze(Q, axes=[1])
      return Q
  
file_path: PARL/benchmark/fluid/MADDPG/simple_model.py
imports: import paddle.fluid
  import parl
  from parl import layers
label_desc: Use image node_id 2 for calling the CriticModel obj's underlying member method code with example usage: obj.value(obs_n, act_n) and returns: Q